The present invention relates to the preparation of silicone compositions having photoactive dyes covalently bonded thereto. In particular, the present invention is directed to specific silicone polymer functional silane dye compounds in which the dye is present in non-diffusible and hydrolytically stable form, thereby rendering these compounds particularly useful in the preparation of in-vitro and in-vivo biological indicator systems.
The use of glass or plastic fibers a fraction of a millimeter in diameter for in vivo biomedical measurements, is a relatively new and important endeavor. Fiber-optic sensors can be as small as electrosensors and offer several distinct advantages. They are safe, involving no electrical connection to the body; the optical leads, very small and flexible, can be included in catheters for multiple sensing; and materials suitable for long term body implantation such as plastics, may be used.
The mechanism of fiber-optic sensor operation is relatively simple. Light from a suitable source travels along an optically conducting fiber to a receptor terminal where reflection, scattering or luminescence occurs. The light emanating from the sensing end of the fiber may be reflected by a tiny transducer that alternatively: (1) Varies the reflectance with some parameter of interest; (2) Back scatters the light due to elements in the medium into which the fiber is inserted; or (3) Absorbs the light, exciting some luminescent species, and returns emitted light of a longer wavelength at an intensity that varies with some component of the system in which the fiber is immersed. The affected light is then returned to a light measurement instrument which interprets the returned signal. Of these three general types of in-vivo fiber-optic sensing mechanisms, the luminescence technique has been recently developed as a measurement to determine the amounts of gasses in blood.
Peterson et al in U.S. Pat. No. 4,200,110 developed a pH sensor as an in vivo device for determination of acidity of the blood. The pH sensor is based on classical acid-based dye indicator chemistry, with a miniature spectrophotometric cell at the end of a pair of optic fibers. In the cell, the dye indicator is covalently bonded to polyacrylamide microspheres so that the terminal is non diffusible, and the sensor reusable. The dye-acrylic polymer composition offers a dye which is present in non-diffusible form but the hydrophilic polymer must be used in the form of gas permeable microspheres in order to function as the spectrophotometric cell of an optic fiber sensor.
The presence of unusually high or low oxygen content in blood samples may indicate various abnormalities. Peterson et al in U.S. Pat. No. 4,476,870 developed an optical sensor for measuring oxygen partial pressure, PO.sub.2. The device is based on the quenching of the fluorescence of certain dyes by oxygen gas. Dyes are chosen for visible light excitation and are distributed on an adsorptive support medium for use as the light scattering terminal for the ingress and egress of optical fiber waves. Generally, a inorganic gas adsorbant, such as silica gel, is used in the dye support medium. However, it has been found that such adsorbant materials are humidity-sensitive, thereby seriously interfering with fluorescence at high humidity.
Because of the importance of fiber-optic gas detecting chemical sensors, a need exists to develop or find materials which can act as molecular support mediums for those dyes which can be used effectively and efficiently in the indicator portions of fiber optic sensors. It has been found that chemically attaching dyes to certain silane compounds provides photoactive center materials which readily react with gas permeable silicone polymers to form non diffusable dye indicator compositions.